You might see discussions of a "contact tank". That gives the chlorine longer to act on its targets. Some are better than others. With your contact tank, you are injecting, and removing the chlorine a short time/distance later.
So would you suggest adding an additional 60 or 80 gallon contact tank to further oxidize the iron? (A 120 gallon fiberglass is too tall for my basement)
Thank you everyone for the advice and information thus far.